bug#40977: --load-path does not honor ~

[Hartmut Goebel]

Specifying the home directory using `~` (tilde) in `--load-path` does
not add the proper path to

Does not work (not who "mypackage":

  guix package --load-path=~/path/tp/my/project -A mypackage

Using $HOME (which si resolve by the shell works:

  guix package --load-path=$HOME/path/tp/my/project -A mypackage


I would expect ~ and ~username to work, too.